Enhanced cholesteryl ester transfer protein activities and abnormalities of high density lipoproteins in familial hypercholesterolemia.

Cholesteryl ester transfer protein may play a role in the cholesteryl ester metabolism between high density lipoproteins (HDL) and apolipoprotein B-containing lipoproteins. To investigate relationship between HDL and cholesteryl ester transfer protein (CETP) activity in the development of atherosclerosis, the present study has focused on CETP activity in the patients with familial hypercholesterolemia (GH). HDL-C and HDL-C/apo A-I mass ratio in heterozygous FH were lower than those in normolipidemic controls. There was a 2-fold increase in total CETP activity in incubated FH serum compared with normolipidemic controls. Assays for CETP activity in the lipoprotein deficient serum (d greater than 1.215 g/ml) were carried out by measuring the transfer of radioactive cholesteryl ester from HDL (1.125 less than d less than 1.21 g/ml) to LDL (1.019 less than d less than 1.060 g/ml). CETP activities in heterozygous FH (79 +/- 4 nmol/ml/h) was significantly higher than those in normolipidemic controls (54 +/- 6 nmol/ml/h). The increased total cholesteryl ester transfer mainly results from increased CETP activity in the d greater than 1.215 g/ml, possibly reflecting an increase in CETP mass in serum. Increased CETP activity in the d greater than 1.215 g/ml was correlated positively with IDL-cholesterol/triglyceride mass ratio (r = 0.496, p less than 0.01), and negatively with HDL-cholesterol/apo A-I mass ratio (r = -0.334, p less than 0.05). These results indicate that the enhanced CETP activities may contribute to increase risk for developing atherosclerosis in FH by changing the distribution of cholesteryl ester in serum lipoproteins.     

The ability of plasma to stimulate fibroblast cholesterol efflux is associated with the -629C-->A cholesteryl ester transfer protein promoter polymorphism: role of lecithin: cholesterol acyltransferase activity

A recent population-based study showed that cholesteryl ester transfer protein (CETP) gene variations, which relate to lower plasma CETP, may predict increased cardiovascular risk, in spite of higher HDL cholesterol. Among other functions, CETP activity contributes to cellular cholesterol efflux, an early step in the anti-atherogenic reverse cholesterol transport (RCT) process. We hypothesized that cellular cholesterol efflux stimulating capacity of plasma could be associated with CETP gene variation. In this study, we tested the extent to which the ability of plasma to promote cholesterol efflux from cultured human fibroblasts is associated with CETP gene variation. In 223 men, the -629C-->A CETP promoter polymorphism, plasma lipids, CETP mass, cholesteryl ester transfer (CET), lecithin:cholesterol acyltransferase (LCAT) activity and the ability of plasma to promote cholesterol efflux from human skin fibroblasts, obtained from a single normolipidemic donor, were determined. In -629CC homozygotes (n=52), cholesterol efflux, plasma CETP mass, CET and LCAT activity were higher, whereas HDL cholesterol was lower compared to -629 AA homozygotes (n=62) and -629CA+AA carriers (n=171) (P<0.05 to P<0.001). Univariate correlation analysis showed that cellular cholesterol efflux was related to CETP genotype (P=0.04), plasma CET (P<0.05), LCAT activity (P<0.001) and apo A-I (P<0.05). Multiple linear regression analysis confirmed the independent association of cellular cholesterol efflux to plasma with CETP genotype. In conclusion, an association of cellular cholesterol efflux with the -629C-->A CETP polymorphism, possibly also involving LCAT activity, could provide a mechanism explaining why CETP gene variation, which relates to lower plasma CETP, does not confer diminished cardiovascular risk.     

I405V and TaqIB polymorphisms of the cholesteryl ester transfer protein and their relation to serum lipid and lipoprotein levels in a Turkish population

Cholesteryl ester transfer protein (CETP) plays a central role in high‐density lipoprotein (HDL) metabolism. Genetic polymorphisms of the CETP gene can influence levels of serum lipoproteins. It has been reported that mean HDL‐cholesterol (HDL‐C) concentrations are low in Turkish population. Thus, we investigated the frequencies of the common I405V and TaqIB polymorphisms of the CETP gene and their relation to serum lipid and lipoprotein levels in a Turkish population. The variant allele frequencies of I405V and TaqIB polymorphisms of the CETP gene were found to be 0.38 and 0.46, respectively and similar to some of the European populations. Subjects for the VV genotype of I405V polymorphism had higher HDL‐C levels than did II subjects. The covariance analysis showed that gender and triglyceride (TG) levels have an effect on the association of HDL‐C and I405V polymorphism. In conclusion, our results indicate that I405V polymorphism may affect the HDL‐C levels in Turkish population. The association of this polymorphism and HDL‐C levels could be modified by other factors, such as gender and TG levels. Copyright © 2009 John Wiley & Sons, Ltd.     

Structure-function studies of human cholesteryl ester transfer protein by linker insertion scanning mutagenesis

Human plasma cholesteryl ester transfer protein (CETP) enhances transfer and exchange of cholesteryl ester (CE) and triglyceride (TG) between high-density lipoprotein and other lipoproteins. To define regions responsible for the neutral lipid transfer activities at the molecular level, a total of 27 linker insertion mutants at 18 different sites along the CETP molecule were prepared and transiently expressed in a mammalian cell line (COS). The inserted linkers were small (usually 6 bp) and did not interrupt the translational reading frame of the CETP cDNA. Although secretion of each mutant protein was less than that of wild-type CETP, the majority of the mutants had normal cholesteryl ester transfer activity (transfer activity per nanogram of CETP in media). However, insertional alterations in three regions severely impaired CE transfer activity: (1) in the region of amino acids 48-53; (2) at amino acid 165; and (3) in the region of amino acids 373-379. Although the impaired activities could also be a result of globally incorrect folding of these CETP mutants, hydrophobicity analysis and secondary structure predictions tended to exclude this possibility for most of the insertion sites at which insertions resulted in inactivation. The insertion at amino acid 379 occurs immediately after a triplet of lysine residues, suggesting that this region might be involved in an essential step in the mechanism of CE and TG transfer, such as the binding of CETP to phosphatidylcholine molecules in the lipoprotein surface. Effects on TG transfer activity were generally similar to those on CE transfer activity, suggesting a similar structural requirement for both neutral lipid transfer activities.     

Increased Serum Cholesteryl Ester Transfer Protein in Obese Children

Objective: To determine whether serum cholesteryl ester transfer protein (CETP), which is one of the physiologically active gene products secreted from adipose tissue, is increased and associated with atherogenic lipoprotein profile in obese children. Research Methods and Procedures: Subjects were 42 consecutive outpatient Japanese obese children, 29 boys and 13 girls, ranging in age from 5 to 14 years, and 25 age‐matched non‐obese children, 13 boys and 12 girls, as the control group for measuring CETP mass. Blood was drawn after an overnight fast and, at the same time, and anthropometric measurements including height, body weight, waist girth, hip girth, and triceps and subscapular skinfold thicknesses were taken. Paired samples were obtained from 15 obese children who underwent psychoeducational therapy. Serum CETP mass was assayed by an enzyme‐linked immunosorbent assay. Results: The serum levels of triglyceride, total cholesterol (TC), low‐density lipoprotein cholesterol, TC/high‐density lipoprotein cholesterol (HDLC), apolipoproteins (apo) B, apo B/apo A₁, and insulin in obese children were significantly higher than the respective reference values. Serum CETP level was ～2‐fold higher (98.7 ± 3.6 vs. 50.9 ± 4.0 nM, means ± SEM, p < 0.001) in the obese children than in the controls. In 15 obese children, whose percentage of overweight declined during therapy, CETP levels decreased significantly. CETP level was correlated with HDLC, TC/HDLC, and insulin, and with percentage of overweight when the data of the obese and non‐obese children were combined. Discussion: CETP is increased and associated with the atherogenic lipoprotein profile in obese children.     

Association of cholesteryl ester transfer protein (TaqIB) and apolipoprotein E (HhaI) gene variants with obesity

Background The pathophysiology of obesity is known to be influenced by alterations in lipid levels. We aimed to evaluate association of cholesteryl ester transfer protein (CETP) and apolipoprotein (APO) E gene variants with asymptomatic obesity. Methods A total of 437 subjects, 159 asymptomatic obese (BMI = 29.29 +/- 3.76) and 278 non-obese (BMI = 23.38 +/- 1.71) individuals, were included in this case-control study. Lipid levels were estimated using standard protocols. Analysis of CETP (TaqIB) and APOE (HhaI) gene polymorphisms was done using PCR-RFLP. Results We found significant difference in blood pressure (systolic, P < 0.0001 and diastolic, P < 0.0001), total cholesterol (P < 0.0001), LDL-cholesterol (P < 0.0001), and HDL-cholesterol (P < 0.0001) in obese as compared to non-obese group. Homozygous APO E4E4 genotype was only observed in 5.7% of obese individuals and none in non-obese group. APO E4 allele carriers were also susceptible for obesity (P = 0.016, OR = 1.73; 95% CI = 1.12-2.68) than non-carriers. Higher blood pressure (Systolic, P = 0.001 and Diastolic, P = 0.004) and triglyceride levels (P = 0.029) were observed in obese subjects with APO E4 allele than individuals without APO E4. However, CETP B1 variant allele carriers did not show alteration in blood pressure and lipid profile in asymptomatic obese subjects. Conclusions APO E4 genotype and allele were found to be associated with asymptomatic obesity, whereas CETP Taq1B polymorphism showed no such association in North Indian subjects.     

Monoclonal antibodies to the Mr 74,000 cholesteryl ester transfer protein neutralize all of the cholesteryl ester and triglyceride transfer activities in human plasma

A cholesteryl ester transfer protein (CETP) of apparent Mr 74,000 has recently been purified from human plasma. Three monoclonal neutralizing antibodies to the CETP were obtained by immunizing mice with purified CETP. The antibodies, each recognizing a similar epitope on CETP, caused parallel and complete immunotitration of plasma cholesteryl ester and triglyceride transfer activities but only partial inhibition of phospholipid transfer activity. Monoclonal immunoaffinity chromatography of plasma or its fractions showed complete removal of cholesteryl ester and triglyceride transfer activities but incomplete removal of phospholipid transfer activity. Sodium dodecyl sulfate gel electrophoresis and immunoblotting of the immunoaffinity-retained fractions showed that only the Mr 74,000 protein was immunoreactive. The results suggest that the previously characterized CETP accounts for all of the cholesteryl ester and triglyceride transfer activity in human plasma but only part of the phospholipid transfer activity.     

CETP and lipid transfer inhibitor protein are uniquely affected by the negative charge density of the lipid and protein domains of LDL

Lipoprotein surface charge influences cholesteryl ester transfer protein (CETP) activity and its association with lipoproteins; however, the relationship between these events is not clear. Additionally, although CETP and its regulator, lipid transfer inhibitor protein (LTIP), bind to lipoproteins, it is not known how the charge density of lipoprotein protein and lipid domains influences these factors. Here, the electronegativity of the protein (by acetylation) and surface lipid (oleate addition) domains of LDL were modified. LDL-only lipid transfer assays measured changes in CETP and LTIP activities. CETP activity was stimulated by <10 microM oleate but completely suppressed by >20 microM. The same electronegative potential induced by acetylation mildly stimulated CETP. Modification-induced enhanced binding of CETP did not correlate with CETP activity. LTIP activity was completely blocked by approximately 10 microM oleate but only mildly suppressed by acetylation. LTIP binding to LDL was not decreased by oleate. Thus, the negative charge of LDL surface lipids, but not protein, is an important regulator of CETP and LTIP activity. Altered binding could not explain changes in CETP activity, suggesting that the extent of CETP binding is not normally rate limiting to its activity. Physiologic and pathophysiologic conditions that modify the negative charge of lipoprotein surface lipids will suppress LTIP activity first, followed by CETP.     

Identification of a sequence within the C-terminal 26 amino acids of cholesteryl ester transfer protein responsible for binding a neutralizing monoclonal antibody and necessary for neutral lipid transfer activity.

The cholesteryl ester transfer protein (CETP; 476 amino acids) mediates the transfer of neutral lipids and phospholipids between plasma lipoproteins. Previous studies showed that the epitope of a neutralizing monoclonal antibody (TP2) was located within the C-terminal 26 amino acids (aa) of CETP. To determine possible involvement of this region in lipid transfer activities, we generated six deletion mutants between Arg-451 and Leu-475 by in vitro mutagenesis and expressed mutant proteins in mammalian cells. Only deletion mutants between aa Phe-463 and Leu-475 failed to bind TP2; these mutant proteins were well secreted by cells but showed markedly reduced cholesteryl ester transfer activity. One of the deletion mutants (delta 470-475) showed similar reductions in cholesteryl ester and triglyceride transfer activities but normal or increased phospholipid transfer activity. Limited proteolysis of this mutant protein indicated a similar overall folding pattern to the wild-type protein. Thus, aa between Phe-463 and Leu-475 are necessary for binding TP2. Deletions within this sequence selectively impair neutral lipid transfer activity, suggesting a direct involvement in neutral lipid transfer.     

Cholesteryl ester transfer protein biosynthesis and cellular cholesterol homeostasis are tightly interconnected

Cholesteryl ester transfer protein (CETP) mediates triglyceride and cholesteryl ester (CE) transfer between lipoproteins, and its activity is strongly modulated by dietary cholesterol. To better understand the regulation of CETP synthesis and the relationship between CETP levels and cellular lipid metabolism, we selected the SW872 adipocytic cell line as a model. These cells secrete CETP in a time-dependent manner at levels exceeding those observed for Caco-2 or HepG2 cells. The addition of LDL, 25OH-cholesterol, oleic acid, or acetylated LDL to SW872 cells increased CETP secretion (activity and mass) up to 6-fold. In contrast, CETP production was decreased by almost 60% after treatment with lipoprotein-deficient serum or beta-cyclodextrin. These effects, which were paralleled by changes in CETP mRNA, show that CETP biosynthesis in SW872 cells directly correlates with cellular lipid status. To investigate a possible, reciprocal relationship between CETP expression and cellular lipid homeostasis, CETP biosynthesis in SW872 cells was suppressed with CETP antisense oligonucleotides. Antisense oligonucleotides reduced CETP secretion (activity and mass) by 60% compared with sense-treated cells. When CETP synthesis was suppressed for 24 h, triglyceride synthesis was unchanged, but cholesterol biosynthesis was reduced by 20%, and acetate incorporation into CE increased 31%. After 3 days of suppressed CETP synthesis, acetate incorporation into the CE pool increased 3-fold over control. This mirrored a similar increase in CE mass. The efflux of free cholesterol to HDL was the same in sense and antisense-treated cells; however, HDL-induced CE hydrolysis in antisense-treated cells was diminished 2-fold even though neutral CE hydrolase activity was unchanged. Thus, CETP-compromised SW872 cells display a phenotype characterized by inefficient mobilization of CE stores leading to CE accumulation. These results strongly suggest that CETP expression levels contribute to normal cholesterol homeostasis in adipocytic cells. Overall, these studies demonstrate that lipid homeostasis and CETP expression are tightly coupled.     

Cholesteryl ester transfer proteins from different species do not have equivalent activities

Site-specific changes in the amino acid composition of human cholesteryl ester transfer protein (CETP) modify its preference for triglyceride (TG) versus cholesteryl ester (CE) as substrate. CETP homologs are found in many species but little is known about their activity. Here, we examined the lipid transfer properties of CETP species with 80–96% amino acid identity to human CETP. TG/CE transfer ratios for recombinant rabbit, monkey, and hamster CETPs were 1.40-, 1.44-, and 6.08-fold higher than human CETP, respectively. In transfer assays between VLDL and HDL, net transfers of CE into VLDL by human and monkey CETPs were offset by equimolar net transfers of TG toward HDL. For hamster CETP this process was not equimolar but resulted in a net flow of lipid (TG) into HDL. When assayed for the ability to transfer lipid to an acceptor particle lacking CE and TG, monkey and hamster CETPs were most effective, although all CETP species were able to promote this one-way movement of neutral lipid. We conclude that CETPs from human, monkey, rabbit, and hamster are not functionally equivalent. Most unique was hamster CETP, which strongly prefers TG as a substrate and promotes the net flow of lipid from VLDL to HDL.     

Plasma cholesteryl ester transfer protein has binding sites for neutral lipids and phospholipids

The plasma cholesteryl ester-transfer protein (CETP, Mr 74,000) promotes exchange of both neutral lipids and phospholipids (phosphatidylcholine, PC) between lipoproteins. To investigate the mechanism of facilitated lipid transfer, CETP was incubated with unilamellar egg PC vesicles containing small amounts of cholesteryl ester (CE) or triglyceride, and then analyzed by gel filtration chromatography. There was rapid transfer of radiolabeled CE or triglyceride and PC from vesicles to CETP. The CETP with bound lipids was isolated and incubated with low density lipoproteins (LDL), resulting in transfer of the lipids to LDL. The CETP bound up to 0.9 mol of CE or 0.2 mol of triglyceride and 11 mol of PC/mol of CETP. para-Chloromercuriphenylsulfonate, an inhibitor of CE and triglyceride transfer, was found to decrease the binding of radiolabeled CE and triglyceride by CETP. Under various conditions the CETP eluted either as an apparent monomer with bound lipid (Mr 75,000-93,000), or in complexes with vesicles. The distribution of CETP between these two states was influenced by the presence of apoA-I or albumin, incubation time, vesicle/CETP ratio, and buffer pH and ionic strength. The results indicate that the CETP has binding sites for CE, triglyceride, and PC which readily equilibrate with lipoprotein lipids and suggest that CETP can act as a carrier of lipid between lipoproteins.     

Lipoprotein lipase enhances the cholesteryl ester transfer protein-mediated transfer of cholesteryl esters from high density lipoproteins to very low density lipoproteins

These studies were undertaken to examine the effects of lipoprotein lipase (LPL) and cholesteryl ester transfer protein (CETP) on the transfer of cholesteryl esters from high density lipoproteins (HDL) to very low density lipoproteins (VLDL). Human or rat VLDL was incubated with human HDL in the presence of either partially purified CETP, bovine milk LPL or CETP plus LPL. CETP stimulated both isotopic and mass transfer of cholesteryl esters from HDL into VLDL. LPL caused only slight stimulation of cholesteryl ester transfer. However, when CETP and LPL were both present, the transfer of cholesteryl esters from HDL into VLDL remnants was enhanced 2- to 8-fold, compared to the effects of CETP alone. The synergistic effects of CETP and LPL on cholesteryl ester transfer were more pronounced at higher VLDL/HDL ratios and increased with increasing amounts of CETP. In time course studies the stimulation of cholesteryl ester transfer activity occurred during active triglyceride hydrolysis. When lipolysis was inhibited by incubating LPL with either 1 M NaCl or 2 mM diethylparanitrophenyl phosphate, the synergism of CETP and LPL was reduced or abolished, and LPL alone did not stimulate cholesteryl ester transfer. These experiments show that LPL enhances the CETP-mediated transfer of cholesteryl esters from HDL to VLDL. This property of LPL is related to lipolysis.     

Influence of insulin sensitivity and the TaqIB cholesteryl ester transfer protein gene polymorphism on plasma lecithin:cholesterol acyltransferase and lipid transfer protein activities and their response to hyperinsulinemia in non-diabetic men.

Lecithin:cholesteryl acyl transferase (LCAT), cholesteryl ester transfer protein (CETP), phospholipid transfer protein (PLTP), and lipoprotein lipases are involved in high density lipoprotein (HDL) metabolism. We evaluated the influence of insulin sensitivity and of the TaqIB CETP gene polymorphism (B1B2) on plasma LCAT, CETP, and PLTP activities (measured with exogenous substrates) and their responses to hyperinsulinemia. Thirty-two non-diabetic men without hyperlipidemia were divided in quartiles of high (Q(1)) to low (Q(4)) insulin sensitivity. Plasma total cholesterol, very low + low density lipoprotein cholesterol, triglycerides, and apolipoprotein (apo) B were higher in Q(4) compared to Q(1) (P < 0.05 for all), whereas HDL cholesterol and apoA-I were lowest in Q(4) (P < 0.05 for both). Plasma LCAT activity was higher in Q(4) than in Q(1) (P < 0. 05) and PLTP activity was higher in Q(4) than in Q(2) (P < 0.05). Insulin sensitivity did not influence plasma CETP activity. Postheparin plasma lipoprotein lipase activity was highest and hepatic lipase activity was lowest in Q(1). Insulin infusion decreased PLTP activity (P < 0.05), irrespective of the degree of insulin sensitivity. The CETP genotype exerted no consistent effects on baseline plasma lipoproteins and LCAT, CETP, and PLTP activities. The decrease in plasma PLTP activity after insulin was larger in B1B1 than in B2B2 homozygotes (P < 0.05). These data suggest that insulin sensitivity influences plasma LCAT, PLTP, lipoprotein lipase, and hepatic lipase activities in men. As PLTP, LCAT, and hepatic lipase may enhance reverse cholesterol transport, it is tempting to speculate that high levels of these factors in association with insulin resistance could be involved in an antiatherogenic mechanism. A possible relationship between the CETP genotype and PLTP lowering by insulin warrants further study.     

Transfer of cholesteryl ester into high density lipoprotein by cholesteryl ester transfer protein: effect of HDL lipid and apoprotein content

Recombinant high density lipoprotein (rHDL) particles were prepared by cosonication of purified lipids and human apoproteins and incubated with partly purified cholesteryl ester transfer protein (CETP) and low density lipoprotein (LDL) containing [3H]cholesteryl ester. Increasing the triglyceride content relative to cholesteryl ester in rHDL significantly decreased the ability of the particles to accept cholesteryl esters transferred by CETP. Kinetic analysis of the data was performed to numerically define the maximum velocity of lipid transfer, Tmax, and the HDL concentration required for half maximal velocity, KH. Increases in rHDL-triglyceride content were shown to result in a significant reduction in the Tmax without a major change in KH. When the free cholesterol content was increased relative to phospholipid, the ability of the particles to accept cholesteryl esters was also decreased in a similar manner. Conversely, rHDL prepared from purified apoprotein A-I, A-II, or mixtures of both, had significantly elevated Tmax and KH values for their interaction with CETP. The results suggest that increases in triglyceride or free cholesterol content of an rHDL particle decrease the catalytic ability of CETP by noncompetitive inhibition. In addition, some component(s) of HDL apoproteins, other than A-I or A-II, were shown to uncompetitively inhibit the activity of CETP, by modifying both Tmax and the KH for the reaction. This study has shown that altered HDL composition may have marked effects on the transfer and equilibration of cholesteryl esters within the HDL pool.     

Description of the torcetrapib series of cholesteryl ester transfer protein inhibitors, including mechanism of action

We have identified a series of potent cholesteryl ester transfer protein (CETP) inhibitors, one member of which, torcetrapib, is undergoing phase 3 clinical trials. In this report, we demonstrate that these inhibitors bind specifically to CETP with 1:1 stoichiometry and block both neutral lipid and phospholipid (PL) transfer activities. CETP preincubated with inhibitor subsequently bound both cholesteryl ester and PL normally; however, binding of triglyceride (TG) appeared partially reduced. Inhibition by torcetrapib could be reversed by titration with both native and synthetic lipid substrates, especially TG-rich substrates, and occurred to an equal extent after long or short preincubations. The reversal of TG transfer inhibition using substrates containing TG as the only neutral lipid was noncompetitive, suggesting that the effect on TG binding was indirect. Analysis of the CETP distribution in plasma demonstrated increased binding to HDL in the presence of inhibitor. Furthermore, the degree to which plasma CETP shifted from a free to an HDL-bound state was tightly correlated to the percentage inhibition of CE transfer activity. The finding by surface plasmon resonance that torcetrapib increases the affinity of CETP for HDL by approximately 5-fold likely represents a shift to a binding state that is nonpermissive for lipid transfer. In summary, these data are consistent with a mechanism whereby this series of inhibitors block all of the major lipid transfer functions of plasma CETP by inducing a nonproductive complex between the transfer protein and HDL.     

Mechanism of cholesteryl ester transfer protein inhibition by a neutralizing monoclonal antibody and mapping of the monoclonal antibody epitope

The plasma cholesteryl ester transfer protein (CETP, Mr 74,000) has a binding site for neutral lipid which can readily equilibrate with lipoprotein cholesteryl esters or triglycerides. Recently, a monoclonal antibody (TP2) was obtained which neutralizes the cholesteryl ester (CE) and triglyceride (TG) transfer activities of the CETP. In this report, the epitope of the inhibitory monoclonal antibody has been localized to a hydrophobic 26-amino acid sequence at the COOH terminus of CETP. The Fab fragments of TP2 caused partial (50%) inhibition of CE transfer and complete inhibition of TG transfer by the CETP. Similarly, the Fab fragments inhibited (37%) the binding of CE to the CETP and abolished the binding of TG to the CETP. Surprisingly, the TP2 Fab was also found to enhance the binding of CETP to plasma lipoproteins and to phospholipid vesicles. In conclusion, the TP2 monoclonal antibody inhibits lipid transfer by blocking the uptake of lipid by CETP. The COOH-terminal epitope may be in or near the neutral lipid binding site. Occupancy of this site by TP2 Fab fragments or by neutral lipid may result in a conformational change of CETP causing enhanced binding to lipoproteins or vesicles.     

Cholesteryl ester transfer protein and its plasma regulator: lipid transfer inhibitor protein.

The interconnections between cholesteryl ester transfer protein (CETP) expression and lipid metabolism, and the possible roles of CETP in atherogenesis are examined. The importance of lipid transfer inhibitor protein in modulating CETP activity is detailed, and the consequences of this inhibitory activity on CETP-mediated events are proposed.     

Increased Plasma Apolipoprotein E-Rich High-Density Lipoprotein and Its Effect on Serum High-Density Lipoprotein Cholesterol Determination in Patients with Familial Hyperalphalipoproteinemia Due to Cholesteryl Ester Transfer Activity Deficiency

Plasma apo E-rich HDL was studied in regard to its quantity and chemical composition in the members of a family with cholesteryl ester transfer activity deficiency, exhibiting familial hyperalphalipoproteinemia. The approach involved a simple precipitation method established in our laboratory. Serum apo E-rich HDL concentrations for two homozygous members were elevated up to 66 and 60 mg/dl in terms of cholesterol (normal, 6.7 ± 2.3 mg/dl, n = 38), and to 9.4 and 10.8 mg/dl in terms of apo E (normal, 2.6 ± 1.5 mg/dl, n = 38). The cholesterol/apo E ratio (mole/mole) of apo E-rich HDL was higher in two homozygotes (669 and 531) than in two cholestatic patients with elevated apo E-rich HDL (268 and 149) and in normal subjects (242 ± 115, n = 38). Chromatographic studies of the serum from a homozygote showed enlargement of all HDL subclasses and apo E in the larger HDL subclass. These facts mndicate that the increase of apo E-rich HDL in this disease occurs secondarily to the enlargement of HDL particles, which require substances to cover their cores, having expanded due to the accumulation of cholesteryl ester. The sera from the homozygotes gave HDL cholesterol concentrations which were remarkably discrepant among commercial precipitating reagents, because of the difference in recovery of apo E-rich HDL with these reagents.     

CETP does not affect triglyceride production or clearance in APOE*3-Leiden mice

The cholesteryl ester transfer protein (CETP) facilitates the bidirectional transfer of cholesteryl esters and triglycerides (TG) between HDL and (V)LDL. By shifting cholesterol in plasma from HDL to (V)LDL in exchange for VLDL-TG, CETP aggravates atherosclerosis in hyperlipidemic APOE*3-Leiden (E3L) mice. The aim of this study was to investigate the role of CETP in TG metabolism and high-fat diet-induced obesity by using E3L mice with and without the expression of the human CETP gene. On chow, plasma lipid levels were comparable between both male and female E3L and E3L.CETP mice. Further mechanistic studies were performed using male mice. CETP expression increased the level of TG in HDL. CETP did not affect the postprandial plasma TG response or the hepatic VLDL-TG and VLDL-apolipoprotein B production rate. Moreover, CETP did not affect the plasma TG clearance rate or organ-specific TG uptake after infusion of VLDL-like emulsion particles. In line with the absence of an effect of CETP on tissue-specific TG uptake, CETP also did not affect weight gain in response to a high-fat diet. In conclusion, the CETP-induced increase of TG in the HDL fraction of E3L mice is not associated with changes in the production of TG or with tissue-specific clearance of TG from the plasma.